Chinese Engine Development

manqiangrexue

Brigadier
The limit isn't the kaboose. It's the intake. And the point isn't to get 15% more thrust through upscaling, but to get that 15% increase in thrust to weight ratio through upscaling, which could require a lot more than a 15% increase in size. This is all academic of course. There are a lot of limiting factors to the logic, and it wasn't my intention to make a straight extrapolation with this point.
J-20's intake was also designed to be able to accommodate WS-15. The engine TWR wouldn't increase at all with upscaling but the TWR of the whole jet will because the thrust would increase by 15% while the weight of the entire jet would only increase by some very small percentage due to the engines making up only a small fraction of the aircraft weight.

As an aside to this debate, to me, engine TWR isn't all that important compared to thrust (assuming that the volume of the engine is limited to a practical size). For example, if you make a 1,000kg engine with 10 tonnes thrust, the TWR is 10. If you install 2 on an 18 tonne jet (no engines) then the TWR of the jet is 1. If you increased the weight of this engine to 1,200kg and the thrust to 11 tonnes, the TWR is lowered to 9.17, but installing 2 of these instead on the 18 tonne frame would result in a TWR of 1.08. Thus, to me, having a nice engine TWR is nice but improving absolute thrust is most important.

Obviously you would need material enhancements to maintain the same level of mechanical performance for a larger engine, but my point is that with a bigger engine you can get more performance with less demanding mechanical performance.
OK, I didn't know that before, but also, the strength to weight ratio would still decrease with upscaling. So... would they cancel out? Who knows?

Also, keep in mind that just because EADS hasn't developed a larger engine that shares the EJ200's performance parameters, that doesn't tell us that they couldn't. They have never needed to because their customers have never asked for a heavy weight fighter engine.
Well yeah, but it also definitely doesn't tell us that they could.
 
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ougoah

Brigadier
Registered Member
You guys are both right in your own ways but practically speaking, Europeans will not have any high performance turbofans for a good decade or so at least. If the WS-15 can offer the J-20 similar performance to f119, well done. If the speculated weight of J-20 is true and it has engines at least as capable as f119, it'll make J-20 even better than any of us would have reasonably hoped for back in 2010 or whenever the prototype was revealed.
 

latenlazy

Brigadier
You guys are both right in your own ways but practically speaking, Europeans will not have any high performance turbofans for a good decade or so at least. If the WS-15 can offer the J-20 similar performance to f119, well done. If the speculated weight of J-20 is true and it has engines at least as capable as f119, it'll make J-20 even better than any of us would have reasonably hoped for back in 2010 or whenever the prototype was revealed.
If the J-20 is really as light as claimed I expect its weight to go up with new engines.
 

Tirdent

Junior Member
Registered Member
Uhhh...Britain, through EADS, has partial ownership of the EJ200. Technologically speaking the EJ200 is definitely more advanced than the WS-10X, and at least from what we know so far it may even be a bit more advanced than the WS-15

Not that I disagree with your premise, but you're confusing a few things here.

Britain's stake in the Eurofighter consortium is via BAE, not EADS - EADS is the French-German-Spanish parent company of commercial aircraft maker Airbus which recently rebranded as... er, Airbus*. That's the airframe side though, the EJ200 engine is the responsibility of another joint-venture named EuroJet in which RR is the British contributor (they practically provided the template with their XG40 demonstrator).

There are $40 RC toy "turbofan" engines with TWR in the teens. By your logic, you could upscale that and end up with a 200kN engine with TWR in the teens.

A scale across so many orders of magnitude faces a number issues, most importantly the centrifugal compressors typical of such small engines would have prohibitive weight and drag (external diameter!) when scaled up. Also, you'd end up with an terrible fuel guzzler, as OPR and turbine inlet temperature are very low.

And that's before we get into aerodynamic issues due to Reynolds number (SNECMA's Silvercrest biz jet engine may currently be running afoul of something like this).

Long story short, scaling by a factor of two is a whole different ball game than scaling by a factor of 10000!

Anyway, those are my thoughts; is there any evidence of this happening? Has anyone scaled an engine up before without material/technological advancements?

Not really with entire engines (it's rare that two aircraft of radically different size have the exact same engine cycle parameter requirements, and if they do it often makes more sense to simply use a higher/lower number of the same basic design), but with individual components it's a very common approach. RR built the Trent 500 for the second generation A340s essentially by taking the core & LPT from the 777's Trent 800, scaling them down and fitting the fan from the Trent 700 (A330) to create an engine with higher BPR and lower thrust than the 700 at the same diameter (limited by ground clearance on the A330/340 wing).

GE has been milking the basic design of the 10-stage, 23:1 PR HPC for the original GE90 for all it's worth since the mid-1990s, first removing a stage from the exit end to increase through put for the more powerful second generation 777 engine (PR reduced to 19, engine OPR was recovered by adding a fourth stage to the new fan/booster system). Then they scaled it down for the GP7200 (A380), followed by a more aggressive scale of the original 10-stage version for the GENx on the 787, to which they've now added a stage to make the GE9X for the 777X!

In fact, I would not be surprised if the 10-stage, 22:1 PR LEAP-1 HPC owes a lot to the same basic design, with performance relaxed a bit to take into account narrowbody engines accumulating cycles (as opposed to hours in cruise) at a higher rate.

I'll believe it when they do it.

RR (well, still Bristol-Siddeley at the time, actually) Olympus in the mid-1960s, with thrust levels of 130 - 150kN.

It was baselined for a number of UK combat aircraft designs - all of these projects were eventually cancelled but the 137kN Mk.320 flew a couple of times in the TSR.2, the 150kN derivative (BS.100 for the VSTOL P.1154) at least made the test bench and of course, it eventually became the 170kN Concorde engine.

* You read that right, the Typhoon is now officially an Airbus! Somehow doesn't quite work in the same way as the Superjet being a Sukhoi, or a Falcon biz jet being a Dassault though :D
 

latenlazy

Brigadier
Not that I disagree with your premise, but you're confusing a few things here.

Britain's stake in the Eurofighter consortium is via BAE, not EADS - EADS is the French-German-Spanish parent company of commercial aircraft maker Airbus which recently rebranded as... er, Airbus*. That's the airframe side though, the EJ200 engine is the responsibility of another joint-venture named EuroJet in which RR is the British contributor (they practically provided the template with their XG40 demonstrator).

Sloppy on my part. I thought the firm working on both the engine and airframe were subsidiaries of the same consortium. Thanks for the clarification.
 

Tirdent

Junior Member
Registered Member
As an aside to this debate, to me, engine TWR isn't all that important compared to thrust (assuming that the volume of the engine is limited to a practical size). For example, if you make a 1,000kg engine with 10 tonnes thrust, the TWR is 10. If you install 2 on an 18 tonne jet (no engines) then the TWR of the jet is 1. If you increased the weight of this engine to 1,200kg and the thrust to 11 tonnes, the TWR is lowered to 9.17, but installing 2 of these instead on the 18 tonne frame would result in a TWR of 1.08. Thus, to me, having a nice engine TWR is nice but improving absolute thrust is most important.

The 18t (sans engines) airframe would not remain at 18t though, since you have to ballast it to keep CoG in range with the heavier engines and beef it up to take the increased thrust as well as greater inertial loads during maneuvers. Although your basic argument holds within certain engine TWR limits, it's a slippery slope where aircraft weight eventually starts to run away.
 
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